Description: (Applicant's Description) Over the last several years, microscopy as a scientific tool has reinvented itself. It has changed from a group of principally descriptive methodologies, to a wide range of primary tools and techniques to investigate the molecular organization of organs, tissues and cells. Advances in microscope and camera design, fluorescent dye technology and the development of fluorescent proteins as well as the advent of inexpensive powerful computers, has made the simultaneous resolution and quantitation of multiple concurrent molecular markers for both protein and DNA at a sub-micron resolution a reality. Furthermore, using these same systems it is possible to probe living cells using a rapidly expanding repertoire of dyes sensitive to changes in cellular pH or the concentration of specific intracellular ions, and to optically section and rebuild images of cells in 3 dimensions using confocal microscopy. The development of nanometer sized particulate markers has been an essential extension of these techniques, allowing the distribution of proteins and mRNA to be studied within cells at a molecular resolution using electron microscopy. The recognition of the potential utility of these techniques to the rapidly expanding research community here at the University of Pittsburgh Cancer Institute (UPCI) led to the formation of a centralized microscope imaging center; the Center for Biologic Imaging (CBI), six years ago. Since then the CBI has become an essential resource for most of the research programs within UPCI. The Center, which forms the Cell and Tissue Imaging Facility within this proposal performs microscopic analyses services for members of the UPCI research community, from the traditional to the cutting edge using a full complement of microscope technologies.